Module 2.2

Question 1

What is the composition of the membrane covering the neuron?

Answer 1

The membrane has two layers that are made up of phospholipids. Inside the phospholipid molecules are cylindrical protein molecules.

Question 2

Describe the structure of the membrane covering the neuron.

Answer 2

The membrane is both flexible and firm and stops chemical from coming in and out of the cell

Question 3

What is meant by selective permeability?

Answer 3

Some chemicals can pass through and some cannot

Question 4

Which chemicals can cross the membrane and which cannot? How do a few biologically important ions cross?

Answer 4

• Oxygen, carbon dioxide, and water can cross.
• Most large or electrically charge ions cannot cross.
• When the membrane is at rest, the sodium channels are closed, preventing almost all sodium flow. Certain kinds of stimulation can open the sodium channels. When the membrane is at rest, potassium channels are nearly but not entirely closed, so potassium flows slowly.

Question 5

What is the sodium-potassium pump? How does the exchange of sodium and potassium lead to an electrical potential across the membrane?

Answer 5

*A protein complex that repeatedly transports sodium ions out of the cell while drawing two potassium ions into it.

Question 6

How does the selective permeability of the membrane increase the electrical potential?

Answer 6

The sodium ions that were pumped out cannot come back in because of the composition of the membrane (selective permeability). But, some of the potassium ions pumped in can get out and when they do they carry their positive charge with them. This increases the electrical gradient across the membrane.

Question 7

Describe the electrical and concentration gradient forces acting on potassium ions.

Answer 7

The electrical gradient pulls potassium in and the concentration gradient pushes it out.

Question 8

What is the advantage of expending energy during the resting state to establish concentration gradients for sodium and potassium?

Answer 8

It maintained the concentration gradients while resting so it is ready to respond strongly.

Question 9

What happens to the electrical potential of the cell if a negative charge is applied? What is this change called?

Answer 9

The negative charge inside the neuron increases. This is called hyperpolarization.

Question 10

What happens to the potential if a small, brief positive current is applied? What is this change called?

Answer 10

Its polarization gets closer to zero. It is caled depolarizing.

Question 11

What happens to the potential if a threshold depolarization is applied?

Answer 11

The ion will open up its sodium channels and ions will come out of it

Question 12

What are “voltage activated sodium channels”?

Answer 12

Channels in the membrane that change permeability depending on the voltage difference across the membrane

Question 13

What causes the initial rapid increase of positivity of the action potential?

Answer 13

When the voltage-gated channels open, the membrane becomes depolarized. Sodium crosses the membrane if depolarization is less than the threshold. The sodium channels open because the potential across the membrane reaches threshold. The sodium ions rush inside the neuron until the membrane’s potential is at reversed polarity.

Question 14

What accounts for the repolarization after the action potential?

Answer 14

Enough potassium ions flow out of the gate and they have a positive charge to drive the membrane beyond the resting state and chloride ions flow inside.

Question 15

What effect does scorpion venom have on the membrane?

Answer 15

It keeps sodium channels open and closes potassium channels.

Question 16

What is the effect of local anesthetic drugs like Novacaine or Xylocaine?

Answer 16

They don’t let sodium ions get through the membrane, therefore preventing action potential.

Question 17

What is the all-or-none-law?

Answer 17

For any neuron under normal circumstances, all action potentials are approximately equal in amplitude and velocity

Question 18

What is the absolute refractory period? What causes it? What is the relative refractory period? What causes it?

Answer 18

It is the first part of the refractory period when the membrane can’t produce an action potential. This happens right after an action potential beause the electric potential is returning from its peak towards the resting point. The relative refractory period is the second part of the refractory period, when a stronger stimulus is needed to start an action potential. This is because the sodium channels are closed and the potassium is coming out of the cell faster than it usually is.

Question 19

How does the action potential propagate down an axon?

Answer 19

A current enters during action potential and depolarizes areas close to it while it flows down an axon

Question 20

What is the major advantage of the myelin sheath? How does the advantage work?

Answer 20

It allows impulses to travel faster and more efficiently. The myein sheath insulates the axon. This combined with the sodium channels producing a positve charge makes the impulse jump to the next node. Without the myelin sheath, the impulses would die out between nodes.

Question 21

What is mean by saltatory conduction?

Answer 21

When action potential jumps from node to node

Question 22

In what ways is transmission by local neurons different from usual conduction by axons?

Answer 22

They don’t follow the all-or-none law. When they are stimulated they hyperpolarize or depolarize only in proportion to the intensity of the stimulus.

Question 23

difference in distribution between ions across membrane

Answer 23

concentration gradient

Question 24

difference in positive and negative charge across a membrane

Answer 24

electrical gradient

Question 25

actively draws in 2 potassium for every 3 sodium is pushes out

Answer 25

Sodium-Potassium pump

Question 26

What type of glia cell synchronizes neuron activity?

Answer 26

astrocytes

Question 27

a difference in electrical charge between the inside and the outside of the cell

Answer 27

electrical gradient

Question 28

The difference in voltage in a resting neuron is called the _______ and is mainly the result of negatively charged proteins inside the cell.

Answer 28

resting potential

Question 29

When the membrane is at rest, sodium channels are ______, preventing all sodium flow

Answer 29

closed

Question 30

When the membrane is at rest, potassium channels are nearly

Answer 30

closed

Question 31

repeatedly transports three sodium ions out of the cell while drawing two potassium ions into it

Answer 31

sodium-potassium pump

Question 32

As a result of the ______________, sodium ions are more than 10x more concentrated outside the membrane than inside, and potassium ions are similarly more concentrated inside than outside

Answer 32

sodium-potassium pump

Question 33

If the charge inside a neuron becomes more negative (at resting potential)

Answer 33

hyperpolarization

Question 34

When the potential reaches ______, the membrane suddenly opens its sodium channels and permits a rapid flow of ions across the membrane.

Answer 34

threshold

Question 35

A ________ is the exaggeration of the usual negative charge within a cell (to a more negative level than usual).

Answer 35

hyperpolarization

Question 36

A ________ is a decrease in the amount of negative charge within the cell.

Answer 36

depolarization

Question 37

A depolarization that passes threshold is an

Answer 37

action potential

Question 38

the membrane proteins that control sodium entry are

Answer 38

voltage-gated channels